1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display (LCD) device and method for fabricating the same that can improve an image quality.
2. Discussion of the Related Art
As demands for portable information devices increase, thin and light flat panel displays (FPDs) are being researched and commercialized and are replacing the conventional cathode ray tubes (CRTs). Liquid crystal display (LCD) devices of the FPDs display images by using an optical anisotropy of liquid crystal molecules. LCD devices are applied to notebooks, desk-top monitors, etc. due to their excellent resolution, color display, picture quality, etc.
A twisted nematic (TN) mode is generally used to drive liquid crystal molecules in a perpendicular direction to the substrates of LCD devices. However, the TN method has a narrow viewing angle of about 90° due to the refractive anisotropy of liquid crystal molecules. That is, because the liquid crystal molecules arranged in a horizontal direction to the substrates are realigned in a vertical direction to the substrates when a voltage is applied, the TN mode LCD devices have a narrow viewing angle.
Accordingly, in plane switching (IPS)-LCD devices have been introduced that have a viewing angle of more than 170° in which the liquid crystal molecules rotate in a horizontal direction of the substrates.
FIG. 1 is a plan view illustrating an array substrate of an IPS-LCD device according to the related art, and FIG. 2 is a cross-sectional view taken along the line I-I′ in FIG. 1.
Referring to FIGS. 1 and 2, the LCD device includes N gate lines 16 and M data lines 17 on an array substrate 10 crossing one another to construct M×N pixels. The LCD device further includes a thin film transistor (TFT) 20 formed adjacent to each crossing of the gate lines 16 and the data lines 17. In the drawings, only one pixel is illustrated for convenience of description.
The TFT 20 includes a gate electrode 21 connected to the gate line 16, a source electrode 22 connected to the data line 17 and a drain electrode 23 connected to a pixel electrode line 18L. The TFT 20 further includes a first insulating layer 15A for insulating the gate electrode 21, the source electrode 22, the drain electrode 23 and an active layer 24 for forming a conductive channel between the source electrode 22 and the drain electrode 23 by a gate voltage applied to the gate electrode 21; and an ohmic-contact layer 25 for ohmic-contacting between the source/drain electrodes 22 and 23 and the active layer 24.
Common electrodes 8 and pixel electrodes 18 are alternately arranged in the pixel region in a direction parallel with the data line 17 for generating a horizontal electric field. The pixel electrodes 18 are electrically connected to the pixel electrode line 18L connected to the drain electrode 23 through a first contact hole 40A formed in a second insulating layer 15B. Also, the common electrodes 8 are electrically connected to a common electrode line 8L arranged in parallel with the gate line 16 through a second contact hole 40B. The common electrodes 8 and the pixel electrodes 18 are formed of a transparent conductive material.
In the LCD device according to the related art, due to their heights, the common and pixel electrodes 8 and 18 protrude from the surface of the second insulating layer 15B that causes a scratch on a surface of an alignment layer during a rubbing process.
More particularly, the rubbing process aligns the molecules of an alignment layer in a desired direction by rotating a roll having a rubbing cloth in a certain direction. When such a protrusion exists below the alignment layer, the rubbing cloth is caught by the protrusion during the rubbing process and the surface of the alignment layer is scratched.
An alignment degree of the scratched portion of the alignment layer is inferior to an alignment degree of other portions of the alignment layer, so that the liquid crystal molecules on the scratched portion may not be aligned in a desired direction. As a result, such a rubbing scratch on the alignment layer decreases the contrast ratio of the LCD device and may be seen as a line defect on the LCD screen.